Ambulatory physiological evaluation system including cardiac monitoring

ABSTRACT

An ambulatory physiological evaluation system including a main and a background gamma radiation detector provided in a vestlike garment worn by a patient for the purpose of monitoring and/or diagnosing the patient&#39;s physiological activities during a prescribed period of time. Also included is an apparatus and method for determining the exact location of the left ventricle of the heart, positioning the main radiation detector relative to the left ventricle, and maintaining the position of the main radiation detector relative to the left ventricle during an ambulatory study period. The ambulatory physiological evaluation system also contains electronic circuitry which monitors and processes information obtained from the radiation detectors. Information from the main and auxiliary detectors, as well as ECG electrodes is recorded on a portable cassette recorder. After the information has been recorded over a desired period of time, the information is presented, through an interface and an analog to digital converter, to the memory of a stand alone computer located in a hospital or office. The computer calculates such items as R-R time intervals, electrocardiagram and time-activity curves, and displays these items and other physiological data for both the main and auxiliary detectors. From the calculations made by the computer, average heart rate, number of aberrant beats, left ventricular ejection fraction and relative cardiac blood volume and other values of physiological significance may be calculated for a time interval of interest.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. Application Ser. No.046,854, filed May 7, 1987, and now U.S. Pat. No. 4,920,969, which is adivisional application of U.S. Ser. No. 785,549, filed Oct. 8, 1985, andnow abandoned, the contents of which is expressly incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to measurement of physiological parametersthrough use of radionuclide detectors, in general, and to an evaluationsystem employing nuclear medicine to monitor and diagnosis a patient'sphysiological activities with the radionuclide detectors and miniatureelectronics being incorporated into a vestlike garment worn outside thechest of the patient.

BACKGROUND OF THE INVENTION

From statistics taken from the American Heart Association, it is knownthat over 40 million Americans have some form of heart and/or bloodvessel disease. Over one million deaths occur annually due tocardiovascular disease, and over 600,000 deaths are the result ofcoronary artery disease. Accurate diagnosis and appropriate therapy arecritical to the management of a patient with cardiovascular disease.

Many diagnostic tools are available to diagnose coronary artery diseaseor heart attack. These include blood tests, electrocardiograms (restingor during stress), angiography (conventional and digital subtractiontechniques), ultrasound and nuclear cardiology techniques. The nuclearcardiology techniques, which employ nuclear imaging, are the onlytechniques capable of functional assessment of the heart. Nuclearcardiology techniques are capable of detecting infractions, ischemia,coronary artery disease, assessment of birth defects and predictingeffectiveness of cardiac medications and/or surgical intervention.

Relative to other diagnostic imaging techniques, nuclear imaging hasseveral important advantages which account for its current growth. Mostimportant, nuclear imaging can provide diagnostic information related tocardiac function rather than just anatomy. By utilizing radioactivetracers, nuclear imaging of left ventricular function (LVF) can monitorphysiological processes over time, whereas most other imaging methodscan produce only a static picture. Therefore, the use of radionuclidesin diagnosis of cardiovascular disease is continually expanding.

In addition to the diagnostic imaging procedure, an important needexists for a device which permits nuclear and ECG measurements to bemade in an ambulatory mode. This need exists because, during theperformance of ordinary activities associated with daily living, leftventricular function varies over a wide range in both the healthy anddiseased heart. These changes in left ventricular function, broughtabout by such ordinary activities as walking, climbing stairs,psychological stress, exposure to severe temperature changes, etc., mayequal or exceed those observed in a laboratory during the performance ofa nuclear cardiac dynamic function study. In coronary artery disease,the accurate and continuous measurement of changes in cardiac physiologysuch as ischemia, arrhythmia, fall in ejection fraction, or a rise inrelative cardiac blood volume can assist in the management of thepatient's disease. In addition, measurements made before and aftersurgery or drug therapy may offer additional insights into the impact ofthese treatments on left ventricular function or dysfunction.

Likewise, in silent ischemia (also defined by many cardiologists as leftventricular dysfunction), where electrocardiographic changes maypossibly be observed after several minutes of ECG recording, leftventricular function changes may be observed in a matter of secondsafter the onset of the decompensation. The effective monitoring of theseleft ventricular changes (such as, increase in end systolic volume)result in better design and administration of a proper therapy regime.

An example of a nuclear cardiac probe designed to meet the need fornoninvasive evaluation of rapidly developing flanges in global leftventricular function is discussed in "The Nuclear Cardiac Probe," by Dr.Henry N. Wagner Jr., Hospital Practice, April 1982, Volume 17, Number 4,pages 163-177. The probe discussed in the article is housed in a consolewhich may be moved by casters from place to place. The probe, however,does not offer a system that can be easily carried by the patient.

Ambulatory monitoring of left ventricular function has been shown to bepossible with the development of a miniaturized system of radionuclidedetectors and electronics incorporated into a vestlike garment and wornoutside the chest. See, for example, "An Ambulatory Ventricular FunctionMonitor: Validation and Preliminary Clinical Results," by Drs. Wilson,Sullivan, Moore, Zielonka, Alpert, Boucher, McKusick and Strauss, TheAmerican Journal of Cardiology, Sept. 1, 1983, Volume 52, pages 601-606.

A truly ambulatory cardiac evaluation system has several potential areasof application. Firstly, it may be particularly useful in evaluating theincidence of silent ischemia. There is now tremendous interest in thecardiology community in the idea that many of the episodes of myocardialischemia in patients with coronary disease are probably pain free. Therehas been much talk that ST segment changes seen on Holter recordings mayrepresent ischemia. That, however, has been extremely controversialbecause people are aware of other circumstances where ST segment changesare not caused by ischemia. Therefore, the issue has been to identifychanges in ventricular function which could be caused by ischemia inassociation with the ST changes. This has been something which is verydifficult to identify in ambulatory subjects. The present invention canmake these measurements at the same time.

The second application is to define the impact of drug therapy. This isparticularly important in patients who have just been diagnosed ashaving coronary disease, hypertension or some other circumstances wherethere is a need to know whether the drug therapy has depressed thepatients ventricular function. The patient can be studied before andafter taking the drug. In both cases, the patient pursues his/her dailyactivities to see whether the drug has negatively impacted cardiacfunction. Currently this is done by merely monitoring the patientsreaction--do they feel tired, get out of breath, etc.

The third area is to define the appropriate exercise prescription inboth people who do not have known heart disease, but are just out ofshape, and in people who have known heart disease. It is particularlyuseful on patients after they have had a myocardial infarction where thepatient should begin exercising on a gradual basis so that they do notexercise to a point where their ventricular function diminishes.

Thus, there is still a need for an ambulatory evaluation system whichcan be worn in relative comfort by a patient for monitoring coronaryartery disease, in surgical and post-operative workups, for anesthesiarehabilitation, for monitoring exercise regime, for drug and dietstudies, and for monitoring the effectiveness of drug administered inthe therapeutic program. The present invention is directed towardfilling that need.

SUMMARY OF THE INVENTION

The present invention relates generally to an ambulatory physiologicalevaluation system including gamma radiation detectors, as cardiacmonitors, utilized in the nuclear medicine field for the purpose ofmonitoring and/or diagnosing a patient's physiological activities, suchas left ventricular function, during a prescribed period of time. In apreferred embodiment of the invention, a compact cardiac monitor havinga main detector is placed generally over the heart of a patient and aradiation detector, mounted within the monitor, senses the ebb and flowof the blood through the heart by detection of the gamma rays emitted byTc^(-99m) labeled blood cells. In order to accurately measure bloodvolume, the radiation detector must be precisely positioned relative tothe heart and this relationship must be maintained during the entiredetecting period. The present invention provides an apparatus and methodfor determining the exact location of the left ventricle of thepatient's heart, positioning the cardiac monitor relative to the leftventricle, and maintaining the position of the cardiac monitor relativeto the left ventricle during an ambulatory study period.

The starting point for the inventive ambulatory physiological evaluationsystem is a vest made of a flexible plastic material, such as"Aquaplast", which contains a pattern of ventilation holes. The vest isadapted to be worn on the torso of a human and contains an arrangementof shoulder straps and belts to provide for a snug, yet relativelycomfortable fit. The vest is worn to provide a base to which a cardiacmonitor including a main detecting device is attached and held in aprecise relationship between the main detecting device and an anatomicalbody, such as the left ventricle of the heart.

Attachment of the cardiac monitor to the vest is accomplished throughthe use of a detector mounting assembly which, in one embodiment is in aform of a mounting bracket which is a lightweight, formed, metallicstructure with means for attaching to both the vest and to the detectingdevice. The mounting bracket fastens two detecting devices, a maindetector and a auxiliary detector, to the vest and provides two meansfor adjusting the main detector relative to the left ventricle of theheart of the wearer. First, the mounting bracket has flanges so that thebracket can be adjusted relative to the vest through fasteners movablypositioned within the vest. Second, for more precise adjustment, themain detector can be adjusted plus or minus one centimeter in twodirections relative to the detector mounting bracket, thereby, providingfor a precise adjustment of the main detector relative to the leftventricle of the heart of the wearer. A scale is provided between themain detector flange and the detector mounting bracket, reading in 5millimeter increments. The scale precisely indicates the relativeposition between the mounting bracket and the main detector.

In order to properly align the detector mounting bracket relative to theleft ventricle of the heart, an alignment fixture is used prior tomounting the main detector to the mounting bracket. The detectoralignment fixture basically comprises a planar leveling plate to whichis fastened a plate within which is embedded a centerline cursor madefrom lead elements. The detector alignment fixture is mounted to theface of the detector mounting bracket with four cap screws. A centerguide pin on the alignment fixture enters a center hole of the detectormounting bracket and, in addition, the four posts on a floating baseplate positioned behind the face of the mounting bracket, enter the fourholes in the alignment fixture. The mounting bracket also has a pair ofopposed flanges which aid in mounting the centerline plate. Aftermounting, the detector alignment fixture is centered on the detectormounting plate.

A conventional scintillation or Gamma camera is brought up to thealignment fixture and adjusted for parallelism. The picture derived fromthe camera on a cathode-ray tube (CRT) display shows the position of thecursor relative to the left ventricle of the heart. If the centerline ofthe cursor is within 10 millimeters of the desired position, any furtheradjustment can be made when the alignment fixture is removed and themain detector assembled to the mounting bracket. If the location of thecenterline is further away from the left ventricle of the heart than 10millimeters, the mount must be readjusted relative to the vest and theabove procedure repeated.

In another embodiment of the invention, a modified mounting bracketstructure is provided which incorporates a ball-type socket carried on amounting plate and into which firstly an alignment fixture can bereleasably clamped for use with a Gamma camera to set the positioning ofthe socket, after which the socket, thus set, can be used to mount amain detector. This embodiment provides somewhat greater flexibility ofadjustment.

The ambulatory physiological evaluation system also contains electroniccircuitry which monitors and processes information obtained from themain and auxiliary detectors. A preferred embodiment of the evaluationsystem basically comprises a Cadmium Telluride (CdTe) detector which isused as the auxiliary detector that is responsive to the presence of asuitable radiopharmaceutical, such as Tc^(-99m) tagged red blood cells,injected into the circulatory system to provide an output signalrepresentative of left lung activity. The CdTe detector may be placed atother locations on the body of the patient to evaluate otherphysiological parameters such as pulmonary, cereberal and muscularfunction. The cardiac monitor that includes the main detector is alsoresponsive to the presence of a suitable radiopharmaceutical injectedinto the circulatory system to produce a signal which is proportionalover the cardiac cycle. The signal produced by the main detector isrepresentative of the left ventricular time activity of the heart. Bothof these signals are fed in analog pulse form to a data logger which ishoused in a bag worn by the patient. The data logger includes thecircuitry necessary to accumulate and manipulate the data and transferit to a portable cassette recording device also housed in the bag. Also,feeding information into the recording device are conventional ECGelectrodes. After the information has been recorded over a desiredperiod of time, the recorded information on cassette is presented,through an impedance matching interface and an analog-to-digitalconverter, to the memory of a stand alone computer located in a hospitalor office. The computer calculates such items as R--R time interval,electrocardiagram and time-activity curves, and displays these items forboth the main and auxiliary detectors. From the calculations made by thecomputer, average heart rate, number of aberrant beats, left ventricularejection fraction and relative cardiac blood volume may be calculatedfor a time interval of interest.

Thus, it is the primary object of the present invention to provide atruly ambulatory physiological evaluation system including cardiacmonitoring.

It is another object of the present invention to provide a mountingapparatus for mounting a radiation detector in a precise relationship toan interior organ of the body of a patient.

It is a further object of the present invention to provide an apparatusto facilitate mounting of a radiation detector to an ambulatory vest ina precise relationship with the left ventricle of the heart of thewearer of the vest.

It is still an object of the present invention to provide a device foraccurately recording information detected by a radiation detector thatis monitoring physiological activity of a patient.

It is yet an object of the present invention to provide an informationprocessing system for manipulating and displaying prerecordedinformation detected by a detector that is monitoring physiologicalactivity of a patient.

Other objects, advantages, and features will become apparent byreference to the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a person operatively wearing anembodiment of the inventive ambulatory physiological evaluation system.

FIG. 2 is a back plan view of the person of FIG. 1 wearing the vest ofthe subject invention without the electronics package and shoulderstrap.

FIG. 3 is a front plan view of the cardiac monitor and mounting bracketfor the evaluation system of FIG. 1.

FIG. 4 is a top view partially in section of the evaluation system ofFIG. 1.

FIG. 5 is a view taken along line 5--5 of FIG. 3.

FIG. 6 is a plan view of the basic elements constituting the vest of theevaluation system of FIG. 1.

FIG. 7 is a view taken along lines 7--7 of FIG. 6.

FIG. 8 is a view similar to FIG. 4 with the cardiac monitor removed andan alternative embodiment for the detector mounting bracket.

FIG. 9 is a front perspective view of the vest of FIG. 1 with thealignment fixture in place on the detector mounting bracket.

FIG. 10 is a top view of the arrangement of FIG. 9.

FIG. 11 is a plan view of the alignment fixture of FIG. 9.

FIG. 12 is a view taken along lines 12--12 of FIG. 11.

FIG. 13 is an exploded perspective view of an embodiment of thecursor-locating plate.

FIG. 14 is a perspective view of a floating base for use mounting itemson the detector mounting plate of FIG. 3.

FIG. 15 is a perspective view of the auxiliary detector used in theevaluation system of FIG. 1.

FIG. 16 is a view taken along lines 16--16 of FIG. 15.

FIG. 17 is a block diagram of the electronic portion of the evaluationsystem of FIG. 1.

FIG. 18a is a schematic diagram of a charge coupled amplifier used inthe electronic portion of FIG. 17.

FIG. 18b is a schematic diagram of a positive peak hold circuit used inthe electronic portion of FIG. 17.

FIG. 19 is a flow chart used to explain the operation of the computerforming part of the evaluation system of FIG. 1.

FIG. 20 is a waveform used in explaining a portion of the operation ofthe electronic portion of FIG. 17.

FIGS. 21 and 22 are waveforms used in explaining a portion of theoperation of the electronic portion of FIG. 17.

FIGS. 23a-23c are waveforms used in explaining a portion of theoperation of the electronic portion of FIG. 17.

FIG. 24 is a front perspective view of a modified vest for use in theinventive system.

FIG. 25 is a rear perspective view of a modified vest.

FIG. 26 is a front perspective view of an operative portion of themodified vest with a modified mounting bracket structure and alignmentfixture secured to the vest.

FIG. 27 is a sectional view on line 27--27 of FIG. 26.

FIG. 28 is a front elevational view of the modified mounting bracketstructure.

FIG. 29 is a rear elevational view of the modified mounting bracketstructure.

FIG. 30 is a rear elevational view of the modified alignment fixture.

FIG. 31 is an enlarged perspective view of a part of the modifiedalignment fixture.

FIG. 32 is a sectional view on line 32--32 of FIG. 28.

FIG. 33 is a perspective view of a spring thrust washer used in themodified mounting bracket structure.

FIG. 34 is a front perspective view of a part of the modified vestshowing a tear-away feature.

FIG. 35 is a front perspective view similar to FIG. 26 but showing themanner in which a main detector is fitted into the modified mountingstructure after removal of the respective alignment fixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Overview of Evaluation System

With reference to FIGS. 1-6, the present invention relates to anambulatory physiological evaluation system, generally designated 10,including gamma radiation detectors 12 and 14 utilized in the nuclearmedicine field for the purpose of monitoring and/or diagnosing apatient's physiological activities during a prescribed period of time.In a preferred embodiment of the invention, a compact cardiac monitor 11including a main detector 12 is placed generally over the heart of apatient and a radiation detector, mounted within the monitor, senses theebb and flow of the blood through the heart by detection of the gammarays emitted by Tc^(-99m) labeled blood cells. In order to accuratelymeasure blood volume, the radiation detector must be preciselypositioned relative to the heart and this relationship must bemaintained during the entire detecting period. The present inventionprovides an apparatus and method for determining the exact location ofthe left ventricle, positioning the cardiac monitor relative to the leftventricle, and maintaining the position of the cardiac monitor relativeto the left ventricle during an ambulatory study period.

With reference to FIGS. 1 through 7, the starting point for theinventive ambulatory physiological evaluation system is a vest 16 madeof a flexible plastic material, such as Aquaplast, which contains apattern of ventilation holes 18. The vest is adapted to be worn on thetorso 20 of a human and contains an arrangement of shoulder straps orshoulder supports 22, 24 and belts 26, 28 to provide for a snug, yetcomfortable fit.

The vest is worn to provide a base to which a detecting assembly in theform of a cardiac monitor 11 is attached and held in a preciserelationship between the detecting device and an anatomical body, suchas the left ventricle of the heart.

Attachment of the detecting device to the vest is accomplished throughthe use of a detector mounting bracket 30 which is a lightweight, formedstructure with means for attaching to both the vest and to the detectingdevice. In a preferred embodiment, the mounting bracket is made fromaluminum, but could be made from plastic or other suitable material. Themounting bracket fastens two detecting devices, the main detector 12 andthe auxiliary detector 14, to the vest and provides two means foradjusting the main detector relative to the left ventricle of the heartof the wearer. First, the mounting bracket has flanges 32 and 34 so thatthe bracket can be adjusted relative to the vest through four fasteners41-44 movably positioned within the vest. Second, for more preciseadjustment, the main detector 12 can be adjusted plus or minus onecentimeter in two directions relative to the detector mounting bracket,thereby, providing for a precise adjustment of the main detectorrelative to the left ventricle of the heart of the wearer. A scale 36 isprovided between the main detector flange and the detector mountingbracket, reading in 5 millimeter increments. The scale preciselyindicates the relative position between the mounting bracket and themain detector.

In order to properly align the detector mounting bracket relative to theleft ventricle of the heart, an alignment fixture 50 is used prior tomounting the main detector to the mounting bracket. The detectoralignment fixture basically comprises an elongated, planar levelingplate 52 to which is fastened a centering plate 54 within which isembedded a centerline cursor made from lead elements 58. The detectoralignment fixture is mounted to the face of the detector mountingbracket with four fasteners, such as cap screws. A center guide pin 60on the alignment fixture enters a center hole 62 of the detectormounting bracket and in addition the four posts 71-74 on a floating baseplate 76 positioned behind the face of the mounting bracket, must enterthe four holes in the alignment fixture 54. The mounting bracket alsohas a pair of opposed, upwardly extending flanges 201 and 203, which aidin aligning and mounting the centering plate. After mounting, thedetector alignment fixture is centered and made parallel with the face162 of the detector mounting plate 30.

A conventional scintillation or Gamma camera (not shown) is brought upto the alignment fixture and adjusted for parallelism. The reason theGamma camera must be adjusted so that its focal plane is parallel to theface of the alignment fixture is because the holes of the collimatorfound in the main detector each have a narrow field of view. The picturederived from the Gamma camera on a cathode-ray tube (CRT) display (notshown) shows the position of the cursor 56 relative to the leftventricle of the heart. If the centerline of the cursor is within 10millimeters of the desired position, any further adjustment can be madewhen the alignment fixture is removed and the main detector 12 assembledto the mounting bracket. If the location of the centerline is furtheraway from the left ventricle of the heart than 10 millimeters, the mountmust be readjusted relative to the vest and the above procedurerepeated.

As shown in FIGS. 17 and 18, the ambulatory physiological evaluationsystem 10 also contains electronic circuitry which monitors andprocesses information obtained from the main and auxiliary detectors. Apreferred embodiment of the evaluation system basically comprises aCadmium Telluride (CdTe) detector 14 which is used as the auxiliarydetector that is responsive to the presence of a suitable radiopharmaceutical Tc^(-99m) tagged red blood cells, injected into thecirculatory system to provide an output signal representative of leftlung or background activity. A cardiac monitor 11 includes the maindetector 12 which is also responsive to the presence of a suitableradiopharmaceutical injected into the circulatory system to produce asignal which is proportional over the cardiac cycle. The signal producedby the main detector is representative of the left ventricular timeactivity of the heart. Both of these signals are fed in analog pulseform to a data logger which is housed in a bag 80 worn by the patient byway of shoulder strap 81. The data logger includes the circuitrynecessary to accumulate and manipulate the data and transfer it to aportable cassette recording device 82, also housed in the bag. Also,feeding information into the recording device are conventional ECGelectrodes 84. After the information has been recorded over a desiredperiod of time, the recorded information is presented, through a tapeplayer 87 an impedance-matching interface 86 and an analog to digitalconverter 88, to the memory 90 of a stand alone computer 92 located in ahospital or office. The computer calculates and analyzes such items asR--R time interval, electrocardiagram and time-activity curves, and/ordisplays these items in eye readable form for both the main andauxiliary detectors. From the calculations made by the computer, suchitems as average heart rate, number of aberrant beats, left ventricularejection fraction and relative cardiac blood volume may be calculatedfor a time interval of interest.

Ambulatory Vest

With reference to FIGS. 1-7, the detailed structure of the ambulatoryvest will now be described. Basically, the vest 16 consists of a onepiece, flexible, thermal plastic material which contains a plurality ofventilation holes 18 arranged in a predetermined pattern to facilitateventilation between the atmosphere and the skin of the wearer when thevest is in its operative position on the torso as shown in FIGS. 1 and2. In a preferred embodiment, the vest is made from a plastic materialsold under the name "Aquaplast".

As shown in FIG. 6, the vest 16 basically comprises an enlarged chestarea 92 that fully covers the chest of the wearer, especially in thearea of the heart. With reference to its orientation on the torso of awearer, the lower portion of the vest on either side of the chestterminates in extended strips 94 and 96. Strip 94 passes below the rightunderarm of the wearer and falls against the small of the back. In likemanner, strip 96 passes below the left arm of the wearer and liesagainst the small of the back. A pair of off-set nylon straps orshoulder supports 26 and 28 are movably positioned within slits 102 and103 defined on strips 94 and 96, respectively. Each of the straps issecured to the edge of a strip by a series of stitches 104 andterminates in an array of Velcro hooks 106 that mate with acomplementary array of Velcro eyes 108 provided on the opposite side ofone of the strip portions.

As shown in FIG. 2, the straps pass across the back of the wearer to theVelcro fastener located on the opposite strip in order to securelyfasten the vest to the patient. Located along a diagonal, at the frontof the vest is an emergency separation or release 110 which is createdby holding mating sides 112 and 114 of the vest in an abuttingrelationship and joining them together by a plastic tape or Velcro 116that is arranged perpendicular to the orientation of the separation line115. Strategically placed guides or planar tabs 113, which are securedto side 114, and guide strip 117 which spans the full length of and issecured to strip 114 facilitates placing sides 112 and 114 in abuttingrelationship. Should the wearer experience any distress during the useof the physiological evaluation system, the vest can be quickly releasedand easily removed through use of the emergency separation 110, whichextends diagonally from the right side of the sternum or breastbone nearthe persons neck downwardly and away from the stomach area toward theright side of the wearer's body. Also defined on the front of the vestare two large apertures 34 and 36 which define open areas in the 4th and5th intercoastal spaces for placement of ECG electrodes in conventionalmanner. The bottom periphery 91 of the vest terminates above the rightchestwall of the wearer to permit ready placement of the ground ECGelectrode.

In order to prevent the vest from moving vertically up and down, thepair of shoulder straps 22 and 24 are provided. Each of the shoulderstraps has the same basic configuration with one strap being the mirrorimage of the other. The straps are generally shaped like an elongatedtriangle, with the base portion 122 having a hole 124 on one side and aslot 126 on the other side. The hole and slot are positioned relative toeach other so that they mate with threaded lugs 125 and 127 definedalong the upper portion of both sides of the front of the vest. Theother end 128 of the strap terminates in a slot 132 which receives abelt 134 that is placed in a mating relationship with a slot 138 definedat the end of strip 96. Also defined in the strap near the forward endis an aperture 142 configured to reveal a sufficient portion of the skinof the patient in order to receive a conventional ECG electrode. Thus,straps 22 and 24 provide spaces for mounting the two clavicle ECGelectrodes.

On the front of the vest, in the area covering the heart, are fourvertically oriented slots 151 through 154. The placement of the slots onthe front of the vest is determined in the following manner. The frontof the vest may be divided in half along the sternum or breastbone ofthe wearer. The four slots are defined along the left side of the vestwith reference to the sternum. About five inches to the left of thesternum and near the nipple area of the wearer, the vest contains acenter point 156. The slots 151-154 exist along a line positioned atabout a 10° angle relative to the horizontal plane H through the centerpoint 156. Each of the slots is approximately one inch in length. Theslots are oriented perpendicular to the 10° line that is defined throughthe center point 156. Alternate pairs of slots 151-153 and 152-154 areapproximately 6.76 inches from each other as measured along a lineparallel to the 10° line. The longitudinal axes of slots 151 and 154 areessentially parallel to each other.

As will be described in greater detail hereinafter, slots 151 through154 are used in connection with the detector mounting bracket 30 toproperly position the cardiac monitor 11 and auxiliary detector 14.

The Detector Mounting Bracket

FIGS. 1, 3, and 4 show the detector mounting bracket 30 in its positionof intended use and mounted on the vest 16. The bracket is made from athin aluminum strip and basically consists of a generally square planarmounting face 162 and a pair of planar mounting flanges 32 and 34.Defined at the center of the planar face 162 is an aperture 62 whichdefines a locating hole used in conjunction with the locating pin 60 ofa detector alignment fixture 50. Also defined at each of the corners ofthe planar surface are larger apertures 171 through 174. Positionedbetween adjacent apertures along each of the edges of the planar surfaceare engraved lines 176 which are typically spaced 5 millimeters apartand define scale 36. These lines are engraved on the surface 162 and areused in conjunction with complimentary marks 178 provided on side faces251 of the main detector 12 in order to properly align the main detectorrelative to the heart of the wearer.

FIG. 4 shows a top view of the mounting bracket secured to the vest withthe cardiac monitor assembly 11 being secured to the mounting bracket.The bracket 30 has the rear face 182 generally flush with a portion ofthe vest 16 so that the planar face 162 is generally perpendicular to aline L that passes through a plane P defined along the sternum of thewearer at an angle of approximately 40° to 50° with an angle of 45°being typical. This position is also referred to as the 45° leftanterior oblique (LAO) position. The outward planar surface 162 of themounting bracket terminates in an bend 192 that continues in a planarportion 184 which is at an approximately 90° angle to the planar face162. The end of planar portion 184 terminates in the flange 32 which isat an approximately 48° angle with reference to the planar portion 162.The opposite bend 194 of the planar surface 162 meets with a planarportion 196 that is at an approximately 381/2° angle with regard to theplanar surface 162. Planar portion 196 terminates in the flange 34 whichis formed at an angle of approximately 141/2° with regard to the planarsurface 162. Both of the flange portions 32 and 34 contain spaced slots202 which are arranged so that when the detector mounting bracket ispositioned on the vest, the longitudinal axes of slots 151 through 154are generally perpendicular to the longitudinal axes of slots 202defined on the mounting bracket. It is intended that the mountingbracket be secured to the vest through a series of wing nut assemblies41 through 44. Each of the wing nut assemblies is made up of a wing nut212 and a threaded portion 214 that terminates at its end in a flat disk216 which is flush against the interior surface 218 of the vest when thewing nut assemblies are mounted. The arrangement of the slots 151through 154 and 202 permit complete two dimensional freedom inpositioning the detector mounting bracket relative to the vest.

In an alternative embodiment of the detector mounting bracket (FIG. 8),the planar position 184 is divided up into two overlapping sections 602and 604 which may move relative to each other to alter the distance fromthe face 162 to the vest 16. The overlapping sections are held togetherby wing nut assemblies 606. At the opposite side of the mountingbracket, flange 34 meets portion 196 through a hinge 610. In this way,the mounting bracket may be securely fastened with the face 162 atseveral different mounting angles without placing any bending stress onthe mounting bracket.

Construction and Mounting of the Main and Background Detectors

As shown in FIGS. 3-5, the main detector 12 is mounted within a housing330 that has a lower portion 332 generally in the shape of a cylinderand an upper portion 334 generally in the shape of an elongatedrectangular solid. The housing is made up of upper and lower shells 336and 338 which are joined together through appropriate fasteners 340 suchas pan screws. Two photo multiplier tubes 344 and 346 are positionednext to each other within the upper housing. The operative ends of thephoto multiplier tubes are in intimate contact with a light guidingprism 348 made of leaded glass. The lower or cylindrical part of thehousing has a cover plate 350 made of black nylon which is screw mountedonto a cylindrically shaped shield 352. The planar surface of the coverplate defines a detecting plane. The part 354 of the shield whichreceives the cover is of narrower diameter than the remaining portion356 of the shield. In a preferred embodiment, the shield is made of leadwith 5% antimony. Positioned next to the cover is an iris 358 made up ofa thin sheet 360 of spring tempered aluminum and a metal ring made fromlead with 5% antimony. The iris is optionally used to restrict the fieldof view in the case of a child's heart or a small adult heart.Positioned next to the iris is a lead collimator 364 having an array ofgamma ray guiding tubes 366. The other side of the collimator isadjacent a sodium iodide (NaI) crystal assembly 368. Between thecollimator and the crystal assembly is a rubber protective gasket 370. Aguide ring 372 made of lead with 5% antimony is in intimate contact withthe lead shield. The guide ring receives and holds a leaded glass window374 adjacent the NaI crystal. Between the glass window 374 and the NaIcrystal 368 is a very thin layer 375 of epoxy or an RTV silicon rubber.The top of the glass window is in communication with one side of thelight prism 348. A connector 380 having a built-in voltage divider andpreamplifier is connected to the photo multiplier tubes. The cable 383is connected to the other side of connector 380 and emerges from thehousing 338 for connection with the circuitry in bag 80.

A generally hollow aluminum monitor base 230 completes the constructionof the main detector. The base has a planar square surface 384 withinthe center of which is defined a large circular aperture having adiameter sized to receive the narrower portion 354 of shield 352. Alsodefined within the surface 384 are four mounting holes 231-234. Furtherdetails of the construction of the main detector 12 may be found inco-pending U.S. Patent Application Ser. No. 711,096 to Suzuki forHigh-Energy Radiation Detector and Method of Detection, which isincorporated by reference.

The way in which the main detector 12 is fastened to the detectormounting bracket 30 will now be described with reference to FIGS. 3-5.In connection with mounting the main detector to the mounting plate, useis made of a floating base plate 76 which may be movably retained to themounting bracket 30 by a suitable means such as a spring or tape. Thebase plate is generally square in configuration with flattened orrounded edges 222 at the corners. At the center of the base plate is anaperture 224 which is of larger diameter than the aperture defined inthe mounting plate. Located at each of the corners is a stand-off, 71through 74, which has a vertical axis oriented perpendicular to theplanar surface 226 of the base plate. Each of the stand-offs isinternally threaded. The base plate, like the mounting bracket is madeof aluminum and is positioned behind the planar surface 162 of themounting bracket in the space defined between the outer surface 228 ofthe vest and the interior surface 182 of the bracket face so that eachof the stand-offs protrude through one of the enlarged apertures171-174. At the same time, the planar face 226 of the base plate is inintimate contact with the interior face 18 of the mounting bracket. Themain detector 12 is supported on base 230 which contains apertures231-234 in each of the corners of the base in order to receive thestand-offs 71 through 74 of the floating base plate. Knurled, threadedlugs 241, 242 are then used to secure the base plate and the maindetector to the mounting bracket. With reference to FIGS. 1 and 3, itcan be seen that the main detector 12 on the base 230 contains four sidefaces 251, each of which bears index mark 178 which is brought intoregistry with one of the scales 36 defined about periphery of thesurface 162 of the mounting bracket. In this way, the main detector maybe mounted anywhere on the surface 162 within plus or minus 10millimeters since each of the scale gradients 176 on the surface 162 are5 millimeters apart.

With reference to FIGS. 3, 15, and 16, the construction and mounting ofthe auxiliary detector will now be described. The auxiliary detectorincludes a cylindrically shaped case 601, the floor of which defines aface 603 for the detector. The opposite end of the case contains athreaded portion 605 which mates with a complimentary threaded portionon a cover plate 608. Together, the case and the cover plate define ahousing within which is mounted the CdTe detector. Positioned within thehousing near the cover 608 is a printed circuit board 610 which containsthe preamplifier circuitry associated with the detector. Mounted in thecircuit board are extended pin contacts 612 and 614. Next to theunderside of the circuit board is a cylindrically shaped hollow leadshield 616. Positioned within the shield is an insulator board 618 andalternate carrier boards 620 and 622. The carrier boards define a squareportion 652 which houses a CdTe chip. The bottom portion of the shieldreceives a cover 626 which has a circular shape to receive a honeycombcollimator 624. At the underside of the cover, near the bottom of thecase, are contact mounting lugs 628 and 630 which receive leads 632. Theleads emerge from the cover of the housing for connection to the datalogger that is contained in the bag 80. The conductive contacts 612 and614 provide electrical contacts with the CdTe chip through the carriers620 and 622.

Since the detector may be used on various parts of the body, it isdesirable to be able to replace and easily remove the detector asdesired. In a preferred embodiment, the face 603 of the detector may becoated with a double stick tape so that the auxiliary detector may beplaced as shown in FIG. 3, on the detector mounting plate or in otherlocations on both the body and the vest.

Location of the Cardiac Monitor

In order to get the most accurate readings from the cardiac monitor, itis imperative that the optimum position of the main detector relative tothe left ventricle be determined and maintained during the detectingperiod. Thus, as part of the present invention, a structure and methodare provided for determining the exact location of the left ventricleand positioning the mounting bracket so that precise placement of themain detector may be insured.

As has already been described, the main detector 12 is secured to thevest through the use of a mounting bracket 30. In a preferredembodiment, the bracket is a light weight formed metallic structure witha series of slots 202 for attaching the bracket to the vest and a seriesof enlarged apertures 171-174 for mounting the cardiac monitor. Thus, itcan be seen that the bracket may be adjustably mounted to the vest andthe main detector may be adjustably mounted to the bracket thusproviding adjustment of the main detector relative to the left ventricleof the heart within two degrees of freedom.

An alignment fixture 50 is employed in order to properly align thedetector mounting bracket relative to the vest. The alignment fixture isgenerally illustrated in FIGS. 9-14. The purpose of the fixture is totransfer a location of an anatomical body, such as the left ventricle ofthe heart, utilizing a conventional scintillation camera.

With reference to FIGS. 9-11, the alignment fixture may be described asfollows. The fixture basically comprises an elongated planar levelingplate 52 on which is mounted a generally square planar cursor-locatingplate 54. Both the leveling plate and the cursor plate are preferablymade of a transparent plastic material. Defined on one side 281 of themid-portion of the planar leveling plate are a series of four holes291-294 aligned to receive the stand-offs 71-74 from the floatingbacking plate 76. Positioned on one surface 296 of the leveling plate isthe cursor or centering plate 54 which also contains four apertures thatare brought into alignment with the apertures 291 through 294 defined inthe leveling plate.

The cursor plate actually consists of two planar portions 302 and 304.Sandwiched between these surfaces are an array of lead cursors 58 whichaid in aligning the detector mounting bracket relative to the leftventricle of the heart. As shown in FIG. 13 the lead cursors generallyconsist of lead slugs which are one millimeter thick and 10 millimeterson a side. The slugs are arranged within evacuated areas defined on amiddle layer 306 in a cross with one cursor 308 being at the center ofthe cross and two cursors 310 and 312 being on either side of the centercursor on the legs of the cross. Together, the cursors define acenterline. All of the lead cursors are the same size with the exceptionof the cursor located on the left as shown in FIG. 11. This cursor 314is 10 millimeters by 20 millimeters and acts as a direction alignmentcursor to identify left and right on any image that includes the cursor.It is to be understood that the three layer construction of the cursorplate is for a preferred embodiment and other methods of constructionwill readily suggest themselves to those skilled in the art.

Emanating from the central portion of the housing is locating pin 60.This pin is brought into registry with the aperture 62 defined in themounting bracket. At the same time, suitable fasteners such as screw 318are used to fasten the leveling plate and the housing to the mountingbracket by passing the fastener through the apertures defined in boththe leveling plate and the housing. The screws are then secured to thethreaded studs provided on the floating backing plate. The detectoralignment fixture is now centered on the detector mount.

A conventional scintillation or Gamma camera (not shown) is brought upto the alignment fixture and adjusted so that the recording plane of thecamera is parallel to the face 281 of leveling plate 52. The cathode-raytube display for the scintillation camera shows the position of the leadcursor array 56 relative to the shadow of the left ventricle of theheart. If the center line of the cursor array is within 10 millimetersof the desired position of the left ventricle of the heart any furtheradjustment can be made with the detector mounting bracket as describedhereinbefore. In this case, the alignment fixture may be removed andreplaced by the main detector 12. If the location of the center line ofthe cursor is further away from the desired portion of the leftventricle then 10 millimeters, the mounting bracket must be readjustedrelative to the vest and the above procedure repeated. The adjustmentrange of the alignment fixture and the mounting bracket may be alteredby changing the distance between gradations on scale 36.

In a preferred embodiment of the subject invention, there is a specificalignment procedure in order to mount the cardiac monitor relative tothe vest and in that way position the cardiac monitor at a certainlocation relative to the left ventricle of the heart.

Initially, a vest which fits the patient is selected. The detectormounting bracket 30 and the floating base plate 76 are secured to thevest. The vest is then placed on the patient and the straps are adjustedto eliminate movement of the vest relative to the body of the patient.The mounting bracket is adjusted so that it is proximately near theheart, some 40° to 45° clockwise using the sternum or breastbone as acenter line. As in the case of the vest, a mounting bracket appropriatefor the patient's body structure is selected.

The floating base plate 76 is positioned so that the studs 71-74 of thebase plate emerge through the large diameter holes 171-174 defined inthe mounting bracket. The alignment fixture is aligned so that the longend of the fixture points to the right side of the patients body (whenlooking at the patient's face). The center pin 60 of the alignmentfixture engages the center hole 62 of the mounting bracket. Thealignment fixture is then secured to the detector mounting bracketthrough the captive fasteners.

The gamma or scintillation camera is then positioned parallel to theface of the alignment fixture and as close as possible to the levelingplate. The Gamma camera is activated in order to observe the position ofthe center line of the alignment fixture relative to the left ventricleof the heart. If the center of the alignment fixture is within 10millimeters of the center of the left ventricle then the Gamma camera isremoved along with the alignment fixture. The cardiac monitor is thenmounted to the mounting bracket.

If the center of the alignment fixture is greater than 10 millimetersaway from the center line of the left ventricle, then the fastenersbetween the mount and the vest are loosened and readjusted to repositionthe mounting bracket and thus alter the position of the center line sothat it is within the 10 millimeters required.

Electronics and Information Processing System

Also forming part of the ambulatory ventricular evaluation system areseveral electronic components. With reference to FIGS. 17, 18a and 18b,a preferred embodiment of the evaluation system basically comprises aCadmium Telluride (CdTe) detector which is used as the auxiliarydetector 14 that is responsive to the presence of a suitableradiopharmaceutical, such as Tc^(-99m) tagged red blood cells, injectedinto the circulatory system to provide an output signal representativeof the left lung time activity. The CdTe detector assembly 14 consistsbasically of a CdTe detector 640, a radiation collimator 624, aradiation shield 616, and a preamplifier. A cardiac monitor 11 thatincludes the main detector 12 is also responsive to the presence of asuitable radiopharmaceutical injected into the circulatory system, andproduces a signal which is proportional to the energy level of radiationemitted by the radiopharmaceutical over the cardiac cycle. The signalproduced by the main detector is representative of the left ventriculartime activity of the heart. Both of these signals are fed in analogpulse form to a data logger, which is housed in a bag 80 worn by thepatient. The data logger includes the circuitry necessary to accumulateand manipulate the data and transfer it to a portable cassette recordingdevice 82 also housing in the bag. Also, feeding information into therecording device are conventional EKG electrodes 84. After theinformation has been recorded over a desired period of time, therecorded information is presented, through a tape player 87, interface86 and an A/D converter 88, to the memory 90 of stand alone computer 92located in a hospital or office for later processing and analysis.

At the heart of the electrical system is a microcomputer 450. In apreferred embodiment, the microcomputer is one produced by NationalSemiconductor and bears the product designation MA2800. Themicrocomputer is a low power, eight bit CMOS microcomputer system. Itprovides a central processing unit, read only memory 451, random accessmemory 453, parallel and serial input/output ports, a system clock,programmable timers, and priority interrupt logic. The microcomputer isused to control the timing and operation of the other circuitryassociated with the ambulatory evaluation system in the manner explainedhereinafter.

FIGS. 17 and 18a show in greater detail the electronic circuitryassociated with the ambulatory ventricular evaluation system. A seriesof Nickel Cadmium batteries 401 provide a voltage and current to avoltage regulator 402 in order to provide a regulated 5 volt DC supply404. The 5 volt regulated supply is used to power up the various circuitelements that make up the evaluation system. In addition, the 5 voltsupply powers up a high voltage power supply 406 in order to produce a1000 volt D.C. signal which is used in conjunction with processing theoutputs from the two photo multiplier tubes 344 and 346 found in thecardiac monitor 11. The outputs from the two photo multiplier tubes arepassed through a high speed charge coupled amplifier 408 and then intothe negative input of a comparator 410 for discriminating signals. Amore detailed discussion of the way in which the cardiac monitoroperates to produce the signal that emerges from charge coupledamplifier may be found in aforementioned U.S Patent Application Ser. No.711,096, which has already been incorporated by reference herein. Thepositive input of the comparator receives a predetermined referencesignal which is typically set at 300 mv. Whenever the output of the highspeed charge coupled amplifier exceeds the reference signal, thecomparator 410 triggers a one shot multivibrator 412 which furthershapes the signal into a four microsecond pulse for introduction into a16-bit counter 414 which is part of the microcomputer 450.

As stated before, the auxiliary detector 14, which is a CdTe detector ispositioned in an appropriate location for intended study. As shown inFIG. 3, the detector is adjacent to, and to the left of the cardiacmonitor 11 on the ambulatory vest 10. The auxiliary detector 14 producesa signal representative of time activity of the area selected for study.With the detector positioned as shown in FIG. 3, the signal produced isrepresentative of left lung time activity. The signal is passed througha charge coupled amplifier 420 and then into a signal discriminator 422.The operation of the charged coupled amplifier may be described asfollows. The charge coupled amplifier is composed of transistors Q1through Q4. The CdTe detector 14 which is biased to 25 volts, produces acharge which is collected at capacitor C4. From there, the signal passesthrough the front end of the charge coupled amplifier 420 which is a lownoise FET amplifier Q6. The output of the FET passes through transistorsQ1 and Q2 which are configured as a high impedance constant current loadto generate an amplified pulse on lead 425. The amplified pulse is fedinto the input of a Darlington amplifier made up of transistors Q3 andQ4. The output of the Darlington amplifier passes along lead 427,through capacitor C9 and resistor R12 into a voltage amplifier 430 whichproduces an output signal of about 40 to 100 millivolts. Thediscriminator 422 is used to convert the output of the charged coupledamplifier into a pulse signal for input into a 12-bit counter 432.Whenever the input into the comparator 434 exceeds the reference signalof about 15 to 100 mv, the output of the comparator is passed to amultivibrator which has been configured as a trigger 436. Every 32milliseconds, the microcomputer takes the nuclear data informationcontained in the 16-bit counter and passes it along the data bus 440 toa digital-to-analog converter 442 in a sequence to generate an amplitudemodulated signal as described below. The counts generated by thebackground detector are accumulated in a 12-bit counter 432 for 8consecutive one second periods. The average of these one second countsis then outputted to the tape recorder on a second track in the formatdescribed below. Since the background count is only one of eightpossible digital channels the data for each channel is stored andoutputted in serial form in the allotted one second slot.

Analog Digital Recording

In the ambulatory cardiac evaluation system of the present inventionlarge quantities of data must be recorded on suitably memory media andsubsequently retrieved for analysis. The nature of the information thatis to be recorded has both A.C. (alternating current) and D.C. (directcurrent) components. Therefore, straight analog recording is notpossible because a conventional tape recorder does not reproduce theD.C. components. In accordance with the present invention, theinformation is recorded on two tracks of the tape recorder. One trackrecords the analog information from D/A converter 442 in an AmplitudeModulation format and the other track records the digital average of theanalog signal in digital format. Before this is done, the microcomputer450 samples the analog signals produced by either the auxiliary detector14 or the main detector 12 above the Nyquist rate. Using the signal fromthe main detector as exemplary, the microcomputer generates an averagedigital value based on the previous n samples. The number of samples nover which the average is taken is suitably selected so as to optimizethe overall frequency response of the signal. This digital value isrecorded on one of the channels of the multichannel tape recorder 82.

Each of the digitized values of the sampled analog signal is thenpresented to a D/A convertor as a positive magnitude corresponding tothe value followed 16 ms later by an equivalent negative value. Ineffect, this is amplitude modulation (A.M.) performed in software. Anenhancement technique is employed to improve the signal-to-noise ratio,whereby a fraction of the average count for the last measurement issubtracted from the current count sample from counter 414. The countingtime period determines the carrier frequency of the amplitudemodulation.

For the purpose of explaining how the data sampling technique is appliedto the inventive ambulatory physiological evaluation system, assume thatthere are n samples/second. For the sake of clarity, also assume thatthese samples represent a signal that is a sinusoidal wave offset by aD.C. value. The graphic representation of this signal after passingthese signals through D/A convertor 442 is shown in FIG. 20. If thisanalog signal were presented to the magnetic tape recorder, the D.C.value would be lost because of the limited bandwidth of the recorder.FIG. 21 shows the same digital sample processed through the D/Aconvertor with each digital sample being presented as a positivemagnitude followed by the equivalent negative magnitude after a timedelay of 16 ms. The result is an amplitude modulated wave.

Applying this signal to the magnetic tape recorder in which the carrierfrequency f₀ lies well within the mid-band of the frequency response ofthe recorder allows full transcription of the A.M. signal. The originalsignal can be recovered by application of standard demodulationtechniques. The demodulated signal is digitized by an analog-to-digitalconverter and then recorded in the memory 90 of the computer 92. The lowfrequency component (D.C. level) obtained from the digital recording isthen added to obtain full reconstruction of the original count fromcounter 414. The demodulator used in a preferred embodiment is apositive peak hold circuit and is shown in FIG. 18b. The demodulation isformed as part of the computer 92. The demodulator basically comprisestwo operational amplifiers 371 and 373. The negative inputs of eachamplifier are connected to each other by way of resistor R16. Thepositive input of amplifier 371 receives the A.M. signal. The output ofamplifier 371 passes through diode D1 and into the positive input ofamplifier 373. The output of amplifier 373 is fed back to the negativeinput of amplifier 373 and also defines the output for the demodulatedsignal. The positive input of amplifier 373 is connected to ground byway of the parallel arrangement of switch S1 and capacitor C15. Eachpositive peak is held by capacitor C15 until the next positivetransition through zero at which point the capacitor charge is dumpedvia switch S1 which is controlled by computer 92. The resultant outputis shown in FIG. 22. The amplitude of each of the held peaks representsthe value of each counting period. These held peaks ultimately aredigitized. Since the peaks are held, the exact timing they are digitizedis not critical. The process of reconstructing the signal is discussedlater.

The frequency of the carrier signal selected is, as mention earlier,also the sampling rate. It should be chosen to exceed the Nyquist rateand also lay in the mid-band of the tape recorder's frequency response.Additionally, the carrier frequency is used to synchronously demodulatethe signal later on.

The digital data output is synchronized to the D/A sampling period. Thismeans that every time a D/A operation is performed on a sample, a bit ofserial data from the parallel serial register 444 is subsequently putout under the control of gate 431. Again, the output is in aReturn-Through-Zero format. This means a "1" is represented as apositive excursion followed by an equal negative excursion and viceversa for a "0". FIGS. 23a-23c show the timing diagram of both D/A andDigital outputs. The digital data uses phase encoding to generate a "1"or a "0". An example of a sequence 1100110 is shown in FIG. 23a. Thedigital data is synchronized to the D/A output waveform (FIG. 23b). Thedigital signal can therefore be demodulated (FIG. 23c) by using the D/Asignal as a phase reference. The implementation of this phase detectionis done using a sample and hold circuit. The digital signal is sampledfor the first 1/4 cycle of the reference D/A output and held till thebeginning of the next cycle as shown. A "1" is represented as positiveheld voltage; a "0" is represented as a negative held voltage.

In order to make best use of the information obtained from theelectronic circuitry associated with the ambulatory physiologicalevaluation system, the cassette recorder 82 has four tracks capable ofrecording information. The tape speed is typically 2 mm per second anddata from the patient may be recorded for up to twenty-four hours. In apreferred embodiment, the frequency response of the recorder is 0.01-100hertz at the nominal tape speed. Track 1 contains the nuclear analogoutput, which is in the form of left ventricular cardiac Beat-to-Beatanalog data. The information is obtained from the D/A converter at asampling rate of 32 Hz. The information is recorded on track 1 in anamplitude modulated format.

Track 2 records eight groups of digital data. The data is processed bythe microcomputer 450 and may consists of any or all of the following:

average nuclear counts;

average auxiliary counts;

secondary auxiliary counts;

event marker and time;

blood pressure;

temperature; and

pulse rate; etc.

The eight groups of digital data are interleaved and a group isoutputted every second. An identifier code proceeds each piece of dataso that the data may be separated later on. Parity checks are includedin the data for error detection. The format is composed of 16-bits ofdata, with 2-bits of parity. The rest of the time left in the one secondtransmission is left as a blank. The blank area is useful in determiningthe beginning of a new word. Track three of the recorder is dedicated torecord one channel of ECG in standard analog fashion. Track four may beused to record the second ECG signal or another physiological signal,such as blood pressure.

Once data has been recorded, the cassette tape is transferred to a fourchannel audio tape recorder where the data is played back at a speedfactor of between 60 and 240. The speed-up is necessary in order tobring the frequency of the ECG recording within the band with of theaudio tape recorder. Since ECG normally has a frequency spectrum ofbetween 0.05 and 100 Hz, the speed-up ratio of 100 or more is needed.

The carrier frequency of the nuclear data is used to initiate thetriggering of a multichannel A/D converter 88. The four channels of theplay back recorder are sequentially multiplexed and made available tothe high speed A/D converter. The A/D converter transfers the datadirectly to hard disk by direct memory access. Some filtering andprocessing of the signals are needed. For these reasons, ananti-aliasing RC filter is required at the output of all four channels.

The digital data acquired on hard disk memory 90 via the high speed A/Dconverter 88 is sorted out by using tags (identifiers associated witheach digital channel), as well as the data sequence itself. Once sorted,the data is compartmentalized and stored as separate files, within thememory of the computer 92. The digital samples representing the nuclearanalog signal are summed and averaged over an eight second period. These8×32 samples are bracketed by two digital channel averages (since oneaverage is recorded every eight seconds). The first digital average isused to reestablish the offsets that were subtracted by the front end.This digital offset was generate to enhance the A/C component of thesignal as mentioned earlier. The current average second digital value isused as the normalizing factor for the detector counts.

Evaluation and Manipulation of Data

After the information from the recording device has been unloaded andstored in the memory 90 of the computer 92, the computer then analyzesand manipulates the data in order to produce a final report. FIG. 19presents a flow diagram showing the various tasks performed by thesoftware contained in the computer. Initially, the computer is poweredup in order to start its operation. A menu appears on the screen withthe following choices:

1. Data Acquisition

2. Data Reduction

3. Identify R-waves

4. Input Patient Data

5. View ECG/Nuclear Data

6. Gross Analysis

7. Beat-to-Beat Analysis

8. Summed Beat Analysis

10. Exit

Selection of the desired function is made by pressing the appropriatenumbered key on the keyboard.

Normally, the first determination to be made is with regard to inputtingpatient data (505). The computer ask the user whether to begin a newpatient (500). If the answer is yes, the computer asks "Does data existfor a previous patient?"(502). If the answer is no, then the computerproceeds to Step-Through-Tape-Reader-Set-Up (504). In this phase ofoperation, the user is stepped through the procedure for setting up thecomputer's tape reader by prompts appearing on the display 91. Thesystem then moves onto the Data Acquisition Step 510, where the data isactually obtained from the cassette tape. Nuclear and ECG data areobtained from the analog to digital converter circuitry and then storedin memory by direct memory access. From the memory, the information isstored on disk. If the answer is yes, the computer goes through anarchiving protocol (506) where information concerning the previouspatient is obtained from a previously recorded file. Certain of the datais then erased (508) and the user is placed into theStep-Through-Tape-Reader-Set-Up. Average data, background data and otherdigital data are also read in simultaneously and stored in files on adisk.

The program may then proceed to Data Reduction 512 where the raw dataread in and written to the files is converted into usable data. Thefirst aspect of the system program is devoted to the conversion ofnuclear data to counts. With regard to ECG data, the program finds eachR-wave peak through the use of look-up tables. R-wave peaks and R-to-Rintervals are written to a file.

After data reduction has been completed, the system program may thenmove on to Gross Analysis 514 and View ECG/Nuclear Data 516 which givesthe user an overall view of the data. No user interaction is needed inthis section. After the analysis is viewed, the user may chose theregions of data to study in detail.

In Gross Analysis, all the data read in is acted on to give a "gross"picture for use in deciding which time periods are of interest forfurther study. A Beat-to-Beat analysis is performed. Heart rate andejection fraction are calculated and averaged every 15, 30 or 60seconds. A graph is then displayed.

Function button inputs from the keyboard 93 are:

1. Background

2. Filtering

3. Start

4. For

5. Average

"Background" is used in calculating ejection fraction which may be themeasured value or percent of the end diastolic count for each beat."Filtering" removes some of the statistical fluctuations and the data iseasier to view. "Start" is the time to start the analysis, in minutes."For" is the time period of the analysis, in minutes. "Average" allowsthe data to be averaged every 15, 30 or 60 seconds. "Running" displays agraph of ejection fraction, heart rate, cardiac output and end diastoliccounts.

This is used to view the nuclear data and ECG for periods of time up to30 seconds. The input buttons from the keyboard 93 are:

1. Filtering

2. Start

3. For

"Filtering" permits the nuclear data to be viewed with or withoutfiltering. Filtering removes some of the statistical fluctuations andmake the data easier to view. "Start" divides the data into 1 minutegroups. Data can only be viewed within a particular 1 minute group."For" provides the number of seconds to view at a time. The limits arebetween 1 second and 30 seconds, however, the computer will not let youselect a time period that goes beyond the end of a minute.

In Time Range 522, the computer sums the data, smooths the data, andsaves it. From the display of raw data, the user indicates a "normalregion". The average R--R interval is obtained from this region. Theuser may input various factors for distinguishing heart beatirregularities. Data is summed by the number of beats or by the timeinterval as decided by the user. The number of beats or the timeinterval for summing is also input by the user. A running average of theR--R interval is taken. Beats which are too long or too short are notused in the summation. Each summed beat is smoothed by using an N pointquadratic smoothing formula (In a preferred embodiment N=15). Thesmoothed data for each summation is saved in a file for later display.

Data analysis proceeds along two branches: Summed Beats 518 andBeat-to-Beat 524. The stored smoothed beats are analyzed. The parametersof interest are found and stored in a file. Some of these parametersare:

Average R--R interval and standard deviation, ejection fraction, errorin ejection fraction, end dyastolic count, end systolic count, time ofend dyastolic count, time of end systolic count, peak ejection, rate andtime of occurrence of end systolic count peak ejection, peak fill, andrate and time of occurrence of peak fill.

Data for each beat is smoothed. The ejection fraction is found from themaximum and minimum of each heart beat. The ejection fraction and R--Rinterval are saved in a file for each heart beat.

As in analysis, presentation branches 530 and 532 according to SummedBeats or Beat-to-Beat. In each case, choices for presentation is madevia function buttons on keyboard 93. The meaning of the buttons aredifferent in the two cases and their usage is shown on the bottom lineof the display screen 91 of the computer.

In a preferred embodiment, the function buttons available on thekeyboard include:

New Parameter

New Time Region

Time Sub-region

Previous Time Region

Histogram

Graph

Histogram & Graph

Print Screen

Print Table of values

Exit from presentation

For all graphs and histograms produced on the display 91 or on theprinter 95, the overall data can be broken up into time periods ofinterest to the user. Appropriate graphs and histograms may be shownsimultaneously.

For both Sum Present (530) and Beat-to-Beat (532), the presentation of anew parameter begins by showing the parameter menu. The followingprocedure also takes place whenever the New Parameter button is pressed.The parameter is shown as a function of time and as histograms. If theparameter chosen is "waveforms", the summed waveforms are displayed.

Data is presented for a new region of time (always within the main timeregion). The user is asked to input the starting and stopping times. Theportion of the patient schedule within the main time region is shown tohelp in the time selection. The data for the current parameter, in thecurrent display type (histogram, graph, or both) is shown. The data fora portion of the current time region is expanded. The user can choosethe region by manipulating the graphics cursor using arrow keys, or caninput starting and stopping time via the keyboard 93. By pressing thePrevious Time Region key, the computer goes back to the previouslychosen time region. This is useful in choosing another Sub-region toexpand.

Three types of display can be chosen via the keyboard 93: Histogram(s)of the data, graph(s) of the data as a function of time, andcombinations of a graph and a histogram. The display is always of themost current parameter using the current time region.

A copy of the display is presented on the screen 91 of the computer,along with any needed explanatory messages. A tabular summary of thedata on the screen can be printed on printer 95.

Exit from the presentation portion may be accomplished after confirmingthat the user really wants to leave the presentation portion. The userwill be given the following choices. Beat-to-Beat data for the same timeperiod 540, new overall time period 542, review gross analysis 544,generate final report 546, archive data 548, leave program 550.

For the Beat-to-Beat data the function buttons on the keyboard include:

New Average

Change Parameter

New Time Region

Time Sub-region

Previous Time Region

Histogram

Graph

Histogram and Graph

Print Screen

Print Table of values

Exit from presentation

Since there are many more points for some data, Beat-to-Beat datapoints, in order to fit on the graph, are averaged as needed.

The new average presentation begins with the selection of a new methodof averaging. The following procedure also takes place whenever the NewAverage button is pressed on the keyboard.

The user is asked whether the running average is to be taken over agiven number of beats or for a given time period. The user then inputsthe number of beats or the time period as selected. A running average ofthe ejection fraction and R--R interval is performed and the resultsstored in a file. A graph and a histogram of ejection fraction and R--Rinterval are shown. The parameters may be changed to ejection fraction,R--R interval, or ejection fraction and R--R interval together. The restof the buttons are the same as for summed data, except that for Exit,the choice is "Summed Data for same time period" 552.

Auxiliary Data consists of the 4 analog inputs plus the second nucleardata counts. This data can be presented along with summed data orBeat-to-Beat data. One or more of these data can be chosen forpresentation. In addition, the data can be presented in graphical and/orhistogram form without the nuclear cardiac data.

A final report summarizing selected features of the study may begenerated. During the Gross Analysis and Gross Presentation portions,the current graphic screen or a table formed from that data may be sentto the printer 95.

Instead of reading in new patient data, the user may begin the sessionby reading in data previously archived (to floppy and/or magnetic tape).The user will then begin the Gross Analysis, and proceed as normal. Atthe end of the session, data may be archived to disk or tape. This canbe used later to review the patient's data. When beginning a session, ifany data is on disk, user is asked if it should be archived, since ithas to be erased for a new patient.

Analysis of ECG waves and presentation of the results is similar toresults and reports from Holter Monitor type instruments. Correlationsare made between ECG and nuclear data.

From the above, it is apparent that many modifications and variations ofthe present invention are possible in light of the above teachings. Forexample, it is contemplated that the present ambulatory physiologicalevaluation system could be used for real-time on-line data analysiswhere an information transmission cable is connected from the datalogger to the computer 92. In this way, information from the main andauxiliary detectors 12 and 14 could be immediately transferred tocomputer 92 for real-time analysis and display. It is also contemplatedthat the bag 80 which carriers the data logger components could bereplaced by a belt that would distribute the weight of the componentscomfortably about the patient's waist.

Modifications Illustrated in FIGS. 24-35

Generally, FIGS. 24-35 show modified versions of the vest, mountingbracket structure and alignment fixture for use in the ambulatoryevaluation system in accordance with the invention.

Thus, referring initially to FIGS. 24, 25 and 34 in particular, there isillustrated a modified vest 600 which may be used in place of the vest16. Vest 600 may again be made of a ventilated flexible plastic materialsuch as Aquaplast, as in the previously described embodiment, and may besimilarly shaped with a relatively wide chest-encompassing front section602, which tapers downwardly at the top so as to fit under the arms andprovide extended rear end portions 604, 606 of narrower width. Toenhance wearer comfort, the vest may be edged with a padded materialedging 608 of foam rubber, plastic or the like. The vest may havecriss-cross adjustable padded shoulder straps 610, 612 which may bereleasably secured at the front of the vest, for example by snapfasteners 614 and which have buckle-type adjusters 616 of known type.The vest further has adjustable length back straps 618, 620 withVelcro-type attachments 622, 624 for securing same around a patient'sbody in similar manner to straps 26, 28 of the previous embodiment.Buckles 626, 628 may be used to adjust the length of the straps totighten or loosen the vest when it is on without releasing the Velcrofastenings.

At the front, vest 600 has a circular aperture 630 (FIG. 24) forpositioning over a patient's heart in like manner to aperture 36 of vest16, and vertically extending slots 632, 634, 636, 638 related in locatedto aperture 630 in like manner to the slots 151-154 of the previousembodiment for adjustably attaching a mounting bracket structure to thevest. Further, the vest has a quick-release breakaway opening on theright hand side (see FIG. 34 in particular) effectively splitting thefront section 602 of the vest into left and right hand segments 602L,602R which are normally held together by quick-release snap fasteners640. An identification tab 642 may be provided adjacent to thequick-release opening.

It is understood that vest 600 can be used in place of vest 16 with themounting bracket structure and alignment fixture as previouslydescribed. Preferably, however, vest 600 may be used with the modifiedmounting structure and alignment fixture shown in FIGS. 26-33, and 35,as will now be described.

The modified mounting structure is denoted generally by reference 644and includes essentially bracket base plates 646, 648, a mounting plate650 supported on plate 648, and universal ball socket assembly 652 onthe mounting plate, into which the alignment fixture 654 and maindetector 656 can be selectively fitted and retained (see respectivelyFIGS. 26, 27 and 35).

Base plate 646 has mutually angled flanges 646a and 646b, flange 646ahaving substantially horizontal slots 658 whereby the plate may beadjustably secured in slots 632, 634 of vest 600 by threaded stud-typeconnectors 660 as in the previous embodiment. Base plate 648 has a vestconnection flange 648a with slots 662 for adjustable securement in vestslots 636, 638 by further threaded connectors 660, and a further angledconnection flange 648b at its opposite end for securement to plate 646by means of still further threaded connectors 660. While not evident inthe drawings, one of the plate flanges 646b or 648b may be slotted toallow a degree of adjustment as between the respective base plates.Between flanges 648a and 648b, the plate 648 has a substantially planarcentral portion 648c for mounting plate 650. Central portion 648c isformed with forwardly projecting upper and lower edge flanges 662, 664,and spaced elongate horizontal slots 666, 668 (see FIG. 29). The baseplates 646, 648 may be of a light weight construction made of materialsgenerally as described in connection with the previous embodiment.

Mounting plate 650 may be of generally rectangular form with beveledcorners and fits between the edge flanges 662, 664. As best seen in FIG.32, the mounting plate is provided with upper and lower rearwardlyprojecting threaded pins 670 which fit in the respective slots 666, 668to allow the position of the mounting plate to be adjusted laterally onthe central portion 648c of plate 648. Screws 672 with operating levers674 are provided on pins 670 to tighten the mounting plate in positionand the levers are provided with angled plastic shrink-on caps 675 whichprotrude forwardly and prevent the levers from dropping behind plate 648and becoming inaccessible. The pitch of the pin and screw threads issuch that only a few degrees of lever movement is required to lock andunlock the mounting plate.

Secured on the outer surface of mounting plate 650 by any suitable meanssuch as adhesive or threaded connectors, is a ball socket support ring677 which has a series of integrally formed forwardly extending flexiblefingers 676, which extend over a circumference of about 315°-330°, thefingers being somewhat concave in profile (see FIGS. 27 and 32) andforming a part cup-like retainer for a similarly profiled generallycylindrical ball socket 678, conveniently made of a hard plasticmaterial. The flexible fingers 676 and the ball socket 678 havecomplimentary concave-convex, inner and outer surfaces whereby thesocket can swivel axially within the fingers and can also be rotatedcircumferentially. However, the ball socket can be locked in positionwithin the retaining fingers by a locking mechanism comprising asubstantially inextensible tightening strap 680 which circumferentiallysurrounds the fingers 676. One end of strap 680 is fixedly secured to afitting 682 on the exterior of ring 674, and the other end of the strapis secured to a retaining band 684 itself attached at a pivot connection686 (FIG. 28) to an over-center, toggle-type latching lever 688 mountedon a support 690 also carried by ring 674. It is understood that bylifting the lever 688, strap 680 is released, loosening the grip of thefingers 676 on ball socket 678 and allowing the socket to rotate andswivel, while lowering the lever with an over-centering action, drawsthe strap closed, tightening the grip of the fingers on the socket andeffectively friction-locking the socket in place.

Internally, socket 678 has a stepped profile (see particularly FIG. 32)with a circumferential rebated groove 690 toward its inner end and threeequally peripherally spaced channels 692 (only one of which is shown inFIG. 32) in the inner peripheral wall of the socket leading into groove690. A thrust washer 694 having a wave-like profile is located in groove690. As previously indicated, socket 678 is adapted selectively toreceive the alignment fixture 654 and the main detector device 656.

The alignment fixture 654 (see FIGS. 27, 30 and 31) comprises agenerally cylindrical body portion 696 to fit in the ball socket 678,and an outer plate portion 698 to provide a datum surface for a Gammacamera as previously described in connection with plate 52 of theprevious embodiment. The cylindrical body portion 698 has a peripheralring 700 provided with three equally interspaced projecting tabs 702 toalign with and engage in the previously referred to channels 692 in thesocket. To releasably fix the fitting in the socket, the tabs 702 arepushed down the channels 692 until they engage and resiliently depressthe thrust washing 694. Then, by twisting the alignment fitting, thetabs can be moved along groove 690 out of the respective channels sothat the fitting is fixed in place by a bayonetting-type action. Whenthe fitting is released, the resilient thrust of washer 694 holds ittightly in place. In order to remove the fitting from the ball socket,it should be depressed against the thrust of the washer, so that tabs702 can be realigned with channels 692.

At is inner end 704, the alignment fitting has a first array of leadinlay elements 706 defining an orthogonal biaxial cursor of the typedescribed in connection with FIGS. 11-13 of the previous embodiment, anda similar sandwich-type cursor structure can be incorporated at theinner end 74 of the alignment fitting. Further, outer plate portion 698of the alignment fitting may be made of a similar sandwich-typeconstruction incorporating a second array of lead inlay elements 708disposed orthogonally as extensions of the first array when viewed inplan as in FIG. 30.

It is understood that the cursor array of lead elements 706, 708 may beused in conjunction with a Gamma camera placed on plate portion 698generally in a similar manner to the previously described embodiment inlocating and targeting an organic target such as a patient's leftventricle. By having separate biplanar cursor arrays 706, 708, however,an additional dimension of accuracy is afforded insofar as if the Gammacamera surface is not placed parallel with plate portion 698, theshadows produced by the respective arrays will not properly align, sothat an indication is also provided as to camera and cursor platealignment.

The main detector device 656 (FIG. 35) is generally similar to the maindetector 11 described in connection with the previous embodiment. Inthis case, however, the detector has a cylindrical body portion withprojecting tabs 710 corresponding to the tabs 702 of the alignmentfitting, for engagement in the channels 692 of the ball socket 678,whereby the detector can be attached to and detached from the ballsocket in like manner to the attachment and detachment of the alignmentfitting.

Use and operation of the modified apparatus may be readily understoodfrom the foregoing. It is evident that firstly, the alignment fittingwill be inserted in the ball socket, and used in conjunction with aGamma camera as in the first embodiment accuratetly to target thepatient's left ventricle, using the available adjustments of themounting structure, namely the lateral movement available to mountingplates 650, the angular adjustments available in base plates 646, 648,and the swivel adjustment available by movement of the ball socket 678.When the patient's ventricle has been accurately targeted, the variousadjustment mechanisms, including strap 680 which locks the ball socketin place, are tightened down, and the alignment fitting is then replacedby the detector device. It is evident that the modified structure has agreater flexibility of adjustment than the previous embodiment.

It is therefore to be understood that, within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed.

What is claimed is:
 1. A vest for use in an ambulatory physiologicalevaluation system, said vest comprising:a flexible, planar vest memberto be worn about the torso of a patient, said member including anenlarged chest area that covers the chest of the wearer, a pair ofstrips disposed on opposite sides of said chest area, each of saidstrips passing below one of the arms of the patient and lying againstthe back of the patient; fist securing means at the end of each stripfor joining the strips to arrange said member about the torso in a snugfit so that the member remains relatively stationary relative to thetorso during movement of the patient; a pair of planar elongated straps,each of said straps spanning across one of the shoulders of saidpatient, one end of each strap terminating in means for movably mountedsaid strap to said chest area, the other end of each strap terminatingin means for securing said strap to one of said strips of said vestmember; quick release means dividing the vest top to bottom in a firstarea of the vest for covering the right side of a wearer's chest; andmounting means on a second area of the vest for apparatus to be used insaid evaluation system, said mounting means being located on a secondarea of the vest for covering a left part of the wearer's chest.
 2. Thevest of claim 1, further comprising:release means along the area of saidmember covering the chest of the patient, said release means defined bydividing said member lengthwise along a line extending from the top ofthe member to the bottom of the member into mating first and secondsides in an abutting relationship; guide means positioned along at leastone of said first and second sides for guiding said sides into saidabutting relationship; and holding means for releasably holding saidfirst and second side in said abutting relationship.
 3. The vest ofclaim 2, further comprising openings defined in said member over thechest of said patient, said openings positioned and sized to expose theskin of the patient for receipt of conventional ECG electrodes.
 4. Thevest of claim 2, wherein said guide means comprises an elongated planarstrip secured to and disposed along said first side of said member, anda plurality of planar tabs secured to and disposed along said secondside of said member, said planar strip and said tabs cooperating tofacilitate joining of said first and second sides in said abuttingrelationships between said planar strip and said tabs.
 5. The vest ofclaim 2 wherein said holding means is at least one Velcro strip disposedacross the abutting relationship of said first and second sides.
 6. Avest for use in an ambulatory physiological evaluatory systemcomprising:a flexible chest member adapted to be worn about the body ofa patient to cover the upper torso including the chest of the patientwith end portions extending under the arms and around the patient'sback; adjustable shoulder strap means adapted to span the patient'sshoulders extending from front to back portions of the vest; adjustableconnector means between the opposite end portions of the vest;quick-release tear-away means dividing the chest member top to bottom onthe right side of the patient's chest into opposed sections; securementmeans for holding the respective sections together; and attachment meanson the left side of the chest member for positioning a heart detector onthe vest to monitor the patient's heart function.
 7. The vest of claim 6wherein the securement means comprises snap fastener means on theopposite sections of the chest member.
 8. The vest of claim 6 which ismade of a perforated flexible plastic material.
 9. A vest for use in anambulatory physiological evaluation system, said vest having mountingmeans for apparatus to be used in said system and comprising:a flexible,planar vest member to be worn about the torso of a patient, said memberincluding an enlarged chest area that covers the chest of the wearer, apair of strip areas integrally formed with and disposed on oppositesides of said chest area, each of said strip areas passing below one ofthe arms of the patient, terminating in a free end lying against theback of the patient, said free ends lying in spaced relation; firstsecuring means extending from the free end of each strip area toward thefree end of the other strip area for joining the strip areas; secondsecuring means at each free end of said strip area for cooperating withthe first securing means extending from the free end of the other striparea to arrange said member about the torso in a snug fit so that themember remains stationary relative to the torso during movement of thepatient; a pair of planar elongated straps, each of said strips spanningacross one of the shoulders of said patient, one end of each strapterminating in means for removably mounting said strap to said chestarea, the other end of said strap terminating in means for securing saidstrap to the back of said vest member; and quick release means along aside area of said member, said release means defined by overlappingportions of said side area and a series of coacting fastenersdistributed lengthwise along a line extending from the top of theoverlapping portions of the side area of the member to the bottom of theoverlapping portions of the side area of the member.